We analyze the kinematics of thick disk and halo stars observed by the Large sky Area Multi-Object Fiber Spectroscopic Telescope. We have constructed a sample of 7,993 F, G and K nearby main-sequence stars (textit{d} $<$ 2 kpc) with estimates of posi
tion (x, y, z) and space velocity ($U$, $V$, $W$) based on color and proper motion from the SDSS DR9 catalog. Three `phase-space overdensities are identified in [textit{V}, $sqrt{U^{2}+2V^{2}}$] with significance levels of $sigma$ $>$ 3. %[L$_{Z}$, eccentricity], [L$_{Z}$, L$_{bot}$], and [V$_{az}$, V$_{triangle}E$]. Two of them (Hyades-Pleiades stream, Arcturus-AF06 stream) have been identified previously. We also find evidence for a new stream (centered at textit{V} $sim$ -180 km s$^{-1}$) in the halo. The formation mechanisms of these three streams are analyzed. Our results support the hypothesis the Arcturus-AF06 stream and the new stream originated from the debris of a disrupted satellite, while Hyades-Pleiades stream has a dynamical origin.
We present a spectroscopically identified catalogue of 72 DA white dwarfs from the LAMOST pilot survey. 35 are found to be new identifications after cross-correlation with the Eisenstein et al. and Villanova catalogues. The effective temperature and
gravity of these white dwarfs are estimated by Balmer lines fitting. Most of them are hot white dwarfs. The cooling times and masses of these white dwarfs are estimated by interpolation in theoretical evolution tracks. The peak of mass distribution is found to be $sim$ 0.6 $M_odot$ which is consistent with prior work in the literature. The distances of these white dwarfs are estimated using the method of Synthetic Spectral Distances. All of these WDs are found to be in the Galactic disk from our analysis of space motions. Our sample supports the expectation white dwarfs with high mass are concentrated near the plane of Galactic disk
We present chromospheric activity index $Srm_{HK}$ measurements for over 13,000 F, G and K disk stars with high signal-to-noise ratio ($>$ 60) spectra in the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) spectroscopic sample. A parameter $delt
a$S is defined as the difference between $Srm_{HK}$ and a `zero emission line fitted by several of the most inactive stars. The $Srm_{HK}$ indices of subgiant stars tend to be much lower than dwarfs, which provide a way to distinguish dwarfs and giants with relatively low resolution spectra. Cooler stars are generally more active and display a larger scatter than hotter stars. Stars associated with the thick disk are in general less active than those of the thin disk. The fraction of K dwarfs that are active drops with vertical distance from the Galactic plane. Metallicity affects $Srm_{HK}$ measurements differently among F, G and K dwarfs in this sample. Using the open clusters NGC 2420, M67 and NGC6791 as calibrations, ages of most field stars in this SDSS sample range from 3-8 Gyr.
Based on high resolution and high signal-to-noise ratio (S/N) spectra analysis of 90 solar type stars, we have established several new metallicity calibrations in Teff range [5600, 6500] K based on red spectra with the wavelength range of 560-880 nm.
The new metallicity calibrations are applied to determine the metallicity of solar analogs selected from SDSS spectra. There is a good consistent result with the adopted value presented in SDSS-DR7 and a small scatter of 0.26 dex for stars with S/N > 50 is obtained. This study provides a new reliable way to derive the metallicity for solar-like stars with low resolution spectra. In particular, our calibrations are useful for finding metal-rich stars, which are missing in SSPP.
We present the chromospheric activity (CA) levels, metallicities and full space motions for 41 F, G, K and M dwarf stars in 36 wide binary systems. Thirty-one of the binaries, contain a white dwarf component. In such binaries the total age can be est
imated by adding the cooling age of the white dwarf to an estimate of the progenitors main sequence lifetime. To better understand how CA correlates to stellar age, 14 cluster member stars were also observed. Our observations demonstrate for the first time that in general CA decays with age from 50 Myr to at least 8 Gyr for stars with 1.0 < V-I < 2.4. However, little change occurs in CA level for stars with V-I < 1.0 between 1 Gyr and 5 Gyr, consistent with the results of Pace et al. (2009). Our sample also exhibits a negative correlation between stellar age and metallicity, a positive correlation between stellar age and W space velocity component and the W velocity dispersion increases with age. Finally, the population membership of these wide binaries is examined based upon their U, V, W kinematics, metallicity and CA. We conclude that wide binaries are similar to field and cluster stars in these respects. More importantly, they span a much more continuous range in age and metallicity than is afforded by nearby clusters.
